The US Senate on Monday confirmed President Barack Obama's pick to head the FBI at a time of heightened scrutiny of US intelligence operations.

James Comey, a respected former deputy attorney general, sailed through on a 93-1 vote, with two senators voting present.

Senator Rand Paul had sought to block Comey but he dropped his opposition to holding a confirmation vote after the Federal Bureau of Investigation responded to his request for clarification on US policy regarding use of domestic surveillance drones.

But the Republican was the lone no vote on the nomination, after the FBI wrote that it did not need a warrant to conduct unmanned aerial vehicle (UAV) operations.

"The FBI today responded to my questions on domestic use of surveillance drones by saying that they don't necessarily need a warrant to deploy this technology," Paul said in a statement.

While he said he disagrees with such an interpretation, he said the FBI's response was sufficient for him to release his hold on the nominee.

The FBI told Paul it has conducted UAV surveillance just 10 times since 2006 over US soil in support of missions related to "kidnappings, search and rescue operations, drug interdictions and fugitive operations."

And it said it has "no plans to conduct general (US) surveillance not related to a specific investigation or assessment."

Comey publicly broke with the Bush White House in 2004 over a secret spy program.

But his positions on George W. Bush administration policies, including the controversial simulated drowning interrogation technique known as waterboarding, and surveillance programs similar to those now used during Obama's presidency, helped rekindle debate in Washington.

"When I first learned about waterboarding, when I became deputy attorney general, my reaction, as a citizen and a leader, was this is torture. It's still what I think," Comey told the Senate panel.

But the 52-year-old lawyer, who has earned plaudits from Democrats for forcing the Bush administration to change parts of its secret surveillance program in 2004, in the past has expressed support for harsh interrogations.

Comey follows the nearly 12-year tenure of Robert Mueller, who until Monday had been the only FBI director of the post-9/11 era.

The FBI is part of the vast US intelligence network that is coming in for criticism for how it scoops up vast amounts of data on Americans, particularly through phone records.

Comey described the gathering of such metadata as "a valuable tool in counterterrorism," but said he wants more transparency in the national security debate.